Washington — It's called "over the horizon" or remote military intervention – the use of unmanned drones and ship-launched missiles to take out human targets operating in a foreign country without having to put boots on the ground.

As the United States departs Iraq after more than eight years of war and occupation, the stepped-up use of remote tactics and light-footprint special operations forces – anything but large-scale, troop-heavy intervention – is just one example of the lasting impact the Iraq war launched in March 2003 is having on American foreign policy.

In other words, instead of wars like Iraq they will be narrow-focused, targeted interventions like those in Pakistan and Yemen. "We're going to focus on killing bad guys," Professor Walt says, "not on trying to reshape entire societies."

When President Obama announced in October that all US military forces will be out of Iraq by the end of the year, the statement marked the end of a decade-old effort designed to remake the Middle East in America's image, with Baghdad as its showcase. The Iraq war was the embodiment of the Bush doctrine, the policy of waging preventive war against a perceived threat.

But as the US military leaves Iraq, the heavy costs incurred in a war that was supposed to be over in a few months are what will remain with policymakers setting American foreign- and national-security policy in the years to come. Defense Secretary Leon Panetta marked the president's Iraq announcement by noting that America's troops and their families had borne the heaviest burden and paid the greatest price in the war. Nearly 4,500 troops were killed on Iraqi soil.

Secretary Panetta might also have underscored that the war has cost the US more than $800 billion at a time of deepening deficits. The price tag for Iraq and Afghanistan combined rises to more than $1.2 trillion.

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The high cost of the war in blood and treasure is certainly the central reason the US won't be launching any Iraq-style invasions anytime soon, most foreign-policy specialists say. But there are others, they add, including the perception that, despite the huge investment, Iraq was in many ways an ill-fated venture.

One way the high financial cost of the Iraq war will shape Washington over the next generation is in spending on defense: It will limit America's options for modernizing the military.

"The Iraq war put a great burden on the Treasury, and contributed significantly to the perilous financial situation we are in today," says James Lindsay, director of studies at the Council on Foreign Relations in Washington. "And that will mean ramifications well into the future, even as we need new planes, new ships, new weapons systems – all of which cost a lot of money."

Yet as significant as the "direct" cost of the Iraq war might be, Mr. Lindsay says that the "indirect" costs on US foreign policy may be even more consequential. In particular, he says, Iraq absorbed America's attention when it should have been focused on China's emergence as a global power.

"I don't want to come across as believing that every failing in US foreign policy stems from the Iraq war, because that's not the case," he says. "But the war was certainly a contributor to a bad habit we have of fixating on one thing and not responding to the major global transformation going on – in this case the rise of China."

Not only Iraq, but also the war in Afghanistan – now entering its second decade – has contributed to the US preoccupation with a region that is not likely to play a significant role in its future prosperity. As GOP presidential aspirant Jon Huntsman Jr. is fond of telling his audiences, "Our future is not in the Hindu Kush mountains of Afghanistan."

Having been consumed by Iraq for the better part of a decade, Lindsay says, the US is now left to play catch-up in a region that will weigh heavily in its future well-being – East Asia. But it will now have to do so, he adds, from an economically weakened condition and with an intervention-weary public wanting to withdraw from the world.

Even some ardent supporters of the invasion of Iraq worry about what it will mean for the US going forward. Robert Lieber, a professor of international relations at Georgetown University in Washington, says the war was a good idea that went awry in execution. He believes if the US hadn't taken out Saddam Hussein, it might soon be dealing with two nuclear powers in the region – Iran and Iraq.

Still, Mr. Lieber says the US is in a phase of turning inward, "and certainly Iraq is part of that picture." The costs the US has incurred from the war "have turned out to be huge – not just in terms of lives and money," he adds, "but to our credibility and for the attention we gave it."

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Perhaps another indirect cost of the war will be in how it tarnished the US military's image as an efficient and almost unlimited tool of American foreign policy.

"There was a sense that the US military was almost magical; it was able to handle any assignment," says Harvard's Walt, listing a string of successes stretching back to the first Gulf War and the Kosovo intervention and including the initial foray into Afghanistan. "But all that ended when it got to the difficult political part after the takeover [in Iraq]. Now we're going to be much more careful about when and where we choose to use the military."

The Bush doctrine may not be dead – as Walt notes, no US president would take preemptive action completely off the table – but it's likely to be a long time before a president turns to the military the way George W. Bush did.

"The idea of preventive war as a doctrine may well join the dustbin of history," says Henri Barkey, a former State Department Iraq analyst now at Lehigh University in Bethlehem, Pa. "Even a Republican president is going to think twice and three times before launching anything close to the Iraq war."

The "new reticence" that will follow Iraq can already be seen in the supportive, partner-dependent role that Mr. Obama chose for the US in NATO's Libya intervention, Mr. Barkey says.

But Libya was only a secondary interest to the US, other experts argue, and lent itself to Obama's approach. The real test of the Iraq war's impact on US foreign policy will come with Iran, these experts say – and perhaps sooner rather than later. For some, reverberations from Iraq can already be seen in the Obama administration's cautious public response to intelligence divulged in a new report by the International Atomic Energy Agency (IAEA), the United Nations' nuclear watchdog arm. The report, released in early November, offers the most detailed evidence yet that Iran is seeking the ability to build and deliver a nuclear bomb.

"We're seeing the impact of the botched intelligence on Iraq in Obama's oh-so-careful approach to intelligence on Iran," says Brookings' Mr. Pollack. "In this case, the Iranians have an acknowledged nuclear program, it's the IAEA that's doing the investigating and making the claims, and yet the initial US response is a muted 'this concerns us' – that's the fallout from Iraq."

But Pollack, a former CIA and National Security CouncilPersian Gulf analyst, says that more than Iran, what worries him most is how the Iraq experience has turned Americans against involvement in the world. That, combined with budget constraints – to some extent the result of a costly Iraq project – could sour Americans on playing a role in places where Pollack says pulling back would be shortsighted.

Egypt is the current example of a "critical American interest" that Pollack uses, though he says there are many others. "We could cut a billion or two in aid to Egypt, which is peanuts in the greater scheme of our deficits, but what happens when the more populist government that's going to emerge says, 'The Americans really are abandoning us. We can do without them?' "

Broadening his argument, Pollack says, "My concern is that, in our post-Iraq fatigue and our mania to focus on internal problems, we'll end up doing things in foreign policy that are penny-wise but very much pound-foolish."